Various industries require removal of contaminants from chemicals before use in subsequent processes or the removal of harmful compounds from chemical prior to discharge of an effluent. Examples of such processes include: use of purifier beds for the removal of contaminants like water vapor from silicon containing process gases used in fiber optic manufacturing; use of dry trains for the removal of unwanted gases like water and oxygen from the re-circulated gas in a closed system such as a glove box; use of a purifier bed for the removal of gases such as amines from the re-circulated environmental gas from a track or photoresist processing cleanroom; and, use of wet scrubbers for the removal of corrosive gases such as ammonia and hydrochloric acid from process gases used in the manufacture of semiconductor wafers.
In many such purification or effluent scrubbing applications the bed is either replaced when its capacity is used up or the bed is regenerated in a separate process that usually requires heating and use of a purge gas. In either case a second purification or scrubbing apparatus is required to maintain continuous process capability or the process is stopped while the purifier is replaced or regenerated.
In dry scrubbers, solid supports such as carbon particles, extruded pellets of iron oxides, copper oxide, alumina, or silica which are reactive with or are impregnated with a reactive chemical reagents designed to remove from a fluid stream gaseous contaminants like HCl, HF, amines, NMP, Cl2, PH3, SiH4 etc. The solid supports are placed in a container or may be bound onto a solid support or membrane. When the capacity of the reagent in the container or on the support is consumed by the contaminant a monitoring device indicates the endpoint capacity of the reactive material. The process is stopped, the used material removed, and a new vessel containing contamination removing material is added.
The reaction reagents of the support or in the support with the contaminant are limited by diffusion. Once the outer portion of the reagent is reacted further reaction is limited by diffusion of contaminant from the outside to the inside of the particle where fresh reactive chemical is present. This diffusion necessitates the use of large volumes of material to efficiently increase gas residence time and prevent premature breakthrough. Typical scrubber beds have a large volume,—55 gallons, which results in a large footprint in the lab. The large volume of the scrubber canisters also leads to a high cost for the waste disposal of the material.
Contamination removal by small meshed particles impregnated with reactive chemical can be a source of particulate contamination. This often necessitates a secondary filter or the manufacture of asymmetric support membranes with smaller pore size than the particles to prevent their loss. This increases the costs of the membrane. Small pore sizes to prevent impregnated particle loss leads to increased pressure drop of gas through the membrane and requires more costly pumps and air handling equipment.
Open beds of reactive material have lower pressure drop but are less efficient at removing contaminants from a gas stream than reactive chemical impregnated in a support particle embedded in a membrane.
It is inconvenient to stop a process to remove the waste or contamination reducing apparatus. Furthermore, endpoint sensors can fail and channeling of the contamination removal beds can occur leading to premature breakthrough.
In effluent scrubbing the wet scrubbers are large footprint devices holding large volumes of water, pumps, Raschig rings and or sprayers to increase mixing and contact area between the effluent gas and the scrubbing liquid.
Sensor located in the scrubber bed give the best indication of breakthrough and permit changeout of the scrubber before breakthrough occurs. However the sensor is typically discarded with the bed which is costly. The types of sensors used in a dry bed is limited. When the sensor is located after the scrubber bed the sensor can be recovered, but breakthrough can occur because the sensor detects only when the bed is exhausted. Breakthrough of the bed can be anticipated and the bed removed prior to consumption, but this leads to inefficient use of the capacity of the scrubber bed and higher costs for bed materials and waste disposal. Undetected breakthrough of the bed can cause product loss or environmental release of toxic gases.
It would be desirable to have a small footprint device useful for the concentration of fluids or removal of contaminants or harmful effluent from fluids to be used in various manufacturing processes and environmental enclosures. It would be further desirable if the purification device were simple to regenerate and enabled continuous processing to occur. It would be further desirable if the device could be used with a wide variety of purification or scrubbing media and reduce the volume of waste generated. There is a need to reduce the volume of chemical waste generated by contamination removal beds and to reduce the size of equipment required for such removal. It would be desirable to improve the mass transfer of contaminants from the gas to the chemically reactive media without increasing the pressure drop of the gas through the bed. It would be desirable to prevent channeling and premature breakthrough of the removal bed or media and to extend the life of the bed to reduce changeout frequency.